The Practical Neurological Examination, Part 6: Testing of Reflex Function

By K. Jeffrey Miller, DC, MBA

Discussion of reflex testing concludes this series on the six primary areas of neurological examination, which also includes mental status, cranial nerves, coordination, and motor and sensory testing.

When performed and interpreted correctly, reflex testing provides the examiner with some of the most object evidence that can be obtained in neurological testing. Deep-tendon, pathological and superficial reflexes all supply a wealth of information on localization and identification of upper and lower motor neuron lesions.

Deep tendon reflexes appear to be straightforward to evoke and interpret. The examiner simply strikes the muscle tendon and rates the response on a scale of 1 to 4.1 Effortless, right? Not really.

The technique of evoking a deep tendon reflex is not as easy as it looks. Examiners often poke or stab the tendon instead of striking it with a swinging motion that allows the hammer to rebound. It takes practice to develop this technique. Proper technique has a lot to do with reflex hammer selection and the grip the examiner uses. There are many different types of reflex hammers,2 most named for the neurologist who developed them. (Table 1) Heavy hammers typically work the best, especially if held at the distal aspect of the handle with a firm but flexible grip. Some hammers have long handles that provide a longer leveler for a firm strike.

Table 1: Types of Reflex Hammers

Hammer Name

Description

Taylor

Probably the most common; rubber triangle, typically red.

Buck

Smaller hammer with heads on either side of differing sizes. A small pin screws into the top and a brush into the bottom of the handle.

Babinski

A wheel with a rubber edge attached to a long plastic or metal hammer.

Dejerine

Similar to the Buck hammer, although the head is the same on both sides; usually there are no attachments and the hammer is much heavier.

Berliner

Looks like an axe; a single head with a long, curved, narrow edge.

Tromner

Has a very large head on one side and a very small head on the opposite side. A heavy hammer.

The strike must be firm; somewhere between treating the patient as if they are fragile and drawing blood. It should hit the tendon directly or the examiner's finger as it palpates and isolates the tendon. This may be uncomfortable for the examiner initially, but with practice the sensitivity decreases. Isolating the tendon with the finger or thumb is preferable to attempting to strike the tendon. Isolation provides a better target (it can actually be seen). The reflex is often more brisk and can be felt.

Isolation of the tendon brings up another common problem with the examiner's ability to elicit a deep tendon reflex: Many examiners can only strike the precise spot with their dominant hand. Some cannot strike the precise spot with either hand. Since the nail bed of the finger or thumb is similar to the size of a nickel, it is recommended that the examiner tape a nickel to a countertop and practice striking it until they can strike the same spot each time with the hammer rebounding appropriately.

Once the examiner has perfected the ability to properly strike the tendon, there may still be times that a reflex is hard to elicit. In these cases, two procedures are recommended. The first is to use a Jendrassik maneuver (basically distract the patient).

For example, if the reflex in question is in the upper extremity, have the patient clench their teeth. If it is in the lower extremity, have the patient clench their fists. Distraction helps bring out the reflex.

The second procedure for a reflex that is hard to elicit is to strike the belly of the muscle. This works well and provides the same information.

As mentioned earlier, interpretation is typically recorded on a scale of 1 to 4. The scale is odd in the fact that normal is in the middle of the scale and not on the high or low end of the scale. (Table 2) There are also different versions of the scale. Some versions have pluses and minuses associated with the numbers, and one version goes from 1 to 5. Scale use may differ between examiners and the interpretation of the degree of reflex may also differ. A normal reflex to one examiner may be interpreted as a decreased reflex to another examiner. The scale has low utility.

Table 2: Deep Tendon Rating Scale

Number

Characteristic of Reflex

Suspected Lesion

0

No reflex

Lower motor neuron

1

Diminished reflex (hyporeflexia)

Lower motor neuron

2

Increased reflex (hyperreflexia)

No lesion

3

Continued motion
("beats" associated with a single strike (clonus)

Upper motor neuron

A better method of reflex interpretation is to use the patient to establish normal and judge by symmetry. Some people have very good reflex responses, while others have very poor reflex responses.

If a person has good responses symmetrically (side to side, upper and lower), then that is probably normal for that person. If a person has poor responses symmetrically, then that is probably normal for that person. Thus, the absence of reflexes is not necessarily pathological. (Note: Lower-extremity deep tendon reflexes are usually a little more responsive than upper-extremity reflexes.)3

If a person has good responses in most muscles, but one muscle provides a decreased response, it is a sign of hyporeflexia. If a person has minimal responses in most muscles, but one muscle provides a greater response, it is a sign of hyperreflexia. Using the patient as their own baseline and symmetry are key factors in diagnosis using deep tendon reflexes.

Final notes on the performance and interpretation of deep tendon reflexes pertains to the number of times a tendon/muscle is struck during testing and the number of responses to each stroke. The examiner should not strike a tendon / muscle once and move directly to the next tendon / muscle. Each tendon / muscle should be struck three to four times with a steady rhythm. This is required because a muscle involved in a lower motor neuron lesion may have a good initial reflex that fades or disappears with succeeding strikes. This cannot be detected using a single strike.

A single response "beat" is expected with each hammer strike. More than one beat from a single strike is termed clonus. This is an indicator of upper motor neuron pathology, especially if the beats exceed three in number.4

The most common and familiar pathological reflex is Babinski's reflex. This is evoked by scraping the plantar aspect of the foot posterior to anterior along the lateral border, then continuing across the ball of the foot. A normal response is no response. If the toes extend and flare the response is abnormal and it is considered a sign of an upper motor neuron lesion. (Note: Babinski's reflex is a normal finding in infants up to 18 months old.)

When Babinski's is recorded in the patient record, it is described as present or absent instead of positive of negative. Some examiners record it as "toes up going" for abnormal responses and "toes down going" for normal responses. This is confusing, as a down-going response is actually a normal plantar reflex and not a normal finding for Babinski's.

While Babinski's reflex is typically the only pathological reflex performed, the examiner should be familiar with other pathological reflexes for purposes of conformation and differential diagnosis. Hoffman's reflex for the hand is a good choice here. This involves the "nipping" of the end of the middle finger as though the examiner is attempting to pinch it off. Normally, there is no response to this action. The abnormal response is flexion of the thumb and fingers.

Hoffman's reflex has the same meaning as Babinski's and is recorded in the same manner: present or absent. The reflex is considered the upper-extremity equivalent of Babinski's. (This fact is frequently the subject of board examination questions.)

The stroke, pinch or general action required to elicit pathological reflexes must be firm. Similar to the method described for the strike for a deep tendon reflex, somewhere between treating the patient as if they are fragile and drawing blood. This is the opposite for superficial reflexes.

Superficial reflexes require a very light contact and action. Lightly stroking the bottom of the foot causing the toes to flex is the plantar reflex. This is why recording the Babinski's reflex as "toes down going" is confusing. "Down-going toes" is a normal plantar reflex, not a normal Babinski's reflex. The ability to apply the correct technique in testing superficial and pathological reflexes often separates the technicians from the doctors.

Superficial reflexes are recorded as present or absent, although these terms have opposite meanings for superficial and pathological reflexes. Present is normal for superficial reflexes and abnormal for pathological reflexes. Absent is abnormal for superficial reflexes and normal for pathological reflexes. Again, the reflexes have an inverse relationship.

The examiner should be familiar with other superficial reflexes. The corneal, pharyngeal and abdominal reflexes are recommended for study, but will not be detailed here.

This concludes the series on neurological testing. Here's to better testing for better diagnosis and patient care.

References

Lanska DJ. The history of reflex hammers. Neurology, 1989;39:1542-1549.

This article is the last of six written to provide practical knowledge and examples of how to incorporate all six components of the neurological assessment into a standard examination in an efficient and productive manner. Part 1 of this series appeared in the Feb. 12, 2011 issue; part 2 appeared in the April 9 issue; and part 3 ran in the June 17 issue; part 4 appeared in the Aug. 12 issue; and part 5 ran in the Sept. 9 issue.